1. Field of the Invention
The present invention relates to a method for detecting a detectably labeled cell or component thereof in a sample comprising one or more cells or components thereof, at least one cell or component thereof of which is detectably labeled with at least two detectable labels, and a system for use in such a method. Immunoassay, fluorescence, and flow cytometry are employed.
2. Description of the Related Art
Various assays for determining qualitative and/or quantitative characteristics of cells or components thereof are known in the art. Flow cytometers, for example, are used in both diagnostics and research laboratories to classify and analyze cells and components thereof. In flow cytometry, cells or components thereof are typically stained with detectable fluorescent labels and are passed in a liquid suspension through a flow cell along with a sheath fluid, such that cells or components thereof are forced by hydrodynamic focusing to flow in single file along the center axis of the flow cell. A focused light beam, such as a laser beam, then illuminates the cells or components as they flow through the examination zone of the flow cell. Optical detectors within the flow cytometer measure certain characteristics of the light as it interacts with the cells or components thereof. Commonly used flow cytometers, such as the Becton-Dickinson Immunocytometry Systems “FACSCAN” (San Jose, Calif.), for example, can measure forward light scatter (generally correlated with the refractive index and size of the particle being illuminated), side light scatter (generally correlated with the particle's size), and fluorescence at one or more wavelengths. Flow cytometers and various techniques for their use are described, generally in “Practical Flow Cytometry” by Howard M. Shapiro (Alan R. Liss, Inc., 1985) and “Flow Cytometry and Sorting, Second Edition” edited by Melamed et al. (Wiley-Liss, 1990).
While flow cytometry techniques have advanced greatly over the years, efficient single-step assay processes for simultaneously detecting multiple types of cells or components thereof, and for simultaneously identifying multiple characteristics of individual cells or components thereof, remain highly desirable in the art. It would be desirable, for example, to have adequate methods and systems for performing reliable and sensitive real-time multiple determinations, simultaneously, through a single or limited step assay process. A capability to perform simultaneous, multiple determinations in a single assay process is known as “multiplexing” and a process to implement such a capability is a “multiplexed assay.”
Conventional flow cytometers, to this point, have yielded a limited capacity to perform real-time multiple determinations. This is due mainly to an inability of conventional flow cytometers to receive, compute, and/or store simultaneous detection data. Moreover, conventional detection and enumeration techniques for cells or components thereof that utilize antibody-conjugated detectable labels typically yield unsatisfactory and unreliable cell or component counts due to antibody aggregations, which yield substantial “false positives.”
Thus, in view of the above, there remains a need for sensitive and reliable methods and systems for the detection and enumeration of cells or components thereof. The present invention seeks to provide such a method and system. These and other objects and advantages of the present invention, as well as additional inventive features, will become apparent to those of ordinary skill in the art upon reading the detailed description set forth herein.